Working on a 1998 Chevy Monte Carlo 3.1L. The problem is the brake pedal is pressing all the way down to the floor and pretty much hits the point of scary when attempting to stop. I have checked the valve going into the power booster and it has vacuum pressure going through it. The fluid level doesn't appear to be low and I found no signs of leaks in the master cylinder, lines, or calipers. The research I have done points to it either being a bad power booster or a bad master cylinder. I have also found alot of conflicting points in my research; mainly in the symptoms of those items going out. Most said the power booster going out will cause a very stiff pedal. Others said it would cause the pedal to hit the floor with minimal stopping power. Most info i have found on the master cylinder going out says it will drop to the floor and have minimal stopping power. Any advice out there that can help me figure out which is the problem? or where to start?

 

Power booster is just what it is. Since you have no external leaks, my bet is the MC is leaking through internally. Seen this issue over alot of years. get yourself a new MC.